Technical
Description

The Canopus-class ships were designed for service in
the Far East, where the
new rising power Japan was beginning to build a powerful and
dangerous navy, and thus had to be able to pass through the Suez Canal. They were
designed to be smaller (by about 2,000 tons), lighter, and faster
than their predecessors, the Majestic-class
battleships, although they were slightly longer at 430 feet (131
m). In order to save weight, the Canopus class carried
less armour than the Majestics, although the change from
Harvey armour in the Majestics to
Krupp armour in
the Canopus class meant that the loss in protection was
not as great as it might have been, Krupp armour having greater
protective value at a given weight than its Harvey equivalent.
Still, their armour was light enough to make them almost
second-class battleships. Part of their armour scheme included the
use of a special 1-inch (2.54 cm) armoured deck over the armour
belt to defend against plunging fire by howitzers that France reportedly planned to
install on its ships, although this report proved to be false.[2]

Right elevation of 12 inch gun turret & ammunition
hoists

Like the Majestics, the Canopus -class ships
had four 12-inch (305-mm) 35-calibre long guns mounted in twin
turrets fore and aft. In the Majestic-class ships HMS
Caesar and HMS Illustrious, these
guns were mounted in circular barbettes that allowed
all-around loading, although at a fixed elevation. The final ship,
HMS
Vengeance, had an improved mounting that also allowed
loading at any elevation; her turret gunhouses also differed from
those of her sisters in being Krupp-armoured and flat-sided, Krupp
armour plates being difficult to curve.[2]
The ships also mounted twelve 6-inch (152-mm) 40-calibre long guns
(sponson mounting allowing some of them to fire fore and aft) in
armoured casemates in addition to smaller guns, and four submerged
18-inch (457-mm) torpedo
tubes.[3]

The Canopus class ships were the first British
battleships with water-tube boilers, which generated more power at less
expense in weight compared with the cylindrical boilers used in
previous ships. The new boilers led to the adoption of fore-and-aft
funnels, rather than the side-by-side funnel arrangement used in
many previous British battleships. The Canopus-class ships
proved to be good steamers, consuming 10 tons of coal per hour at
full speed,[4] with a
high speed for battleships of their time, a full two knots faster
than the Majestics.[5]